Data storage devices typically store data on a storage medium, which will be accessed by a read-write mechanism many times over the life of the storage device. As used herein, the term “storage device” refers to any apparatus adapted to store data electronically or magnetically, including disc drives, flash memory, read-only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), probe storage devices, and the like.
Over the lifetime of a storage device, a read-write mechanism of the storage device can experience wear and tear, causing a gradual deterioration of the performance of the read-write mechanism. Deterioration of the read-write mechanism can include reduced signal amplitude, undesired inter-symbol (or inter-track) interference, excessive noise, unanticipated changes in magnetic field area, misalignment of the read/write mechanism, and numerous other problems, any of which can lead to data errors and/or to failure of the storage device. For example, shock events, such as physically dropping the storage device, can cause the read-write mechanism to contact the storage medium or can cause misalignment of the read-write mechanism. Additionally, thermal events, such as thermal aspersities, can cause wear in the read-write mechanism. As used herein, the term “thermal asperity” refers to a large voltage generated in the read-write mechanism by contact with the storage medium of the storage device.
Deterioration of the read-write mechanism leads to degradation of the signal quality of an associated read channel, which directly translates into inferior quality of service (QoS) and shortened device lifetime of the storage device. Quality of service (QoS) refers to a guarantee of a minimum standard of quality for information contained within a signal. Devices that support QoS-guarantees typically provide different levels of quality depending on which type of data is being processed, such as voice, data or video. For example, in one instance, a higher quality of service may be required for video storage and retrieval (e.g. constant stream of data) than is required for sending and receiving other types of data (such as sound). In some communication protocols, quality of service is maintained using a combination of parity bit checking, error checking, encoding and handshaking. Typically, QoS is maintained using software and/or hardware of a host system. Unfortunately, read mechanism deterioration can undermine QoS if information received under QoS-guarantees is stored on a storage device using a degraded read-write mechanism, which can introduce errors into the information stream due to physical deterioration.
There is ongoing need for storage devices that can support QoS guarantees for different types of information. Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.